Replacing Strings Java

I have this function to check if some words appear in a specific line, and then surround them with a given char.

The code above works like a charm, however since the words in the string array "words" are always low case, the words will be lower case as well. How can i fix this issue ?

The inputs:

BufferedReader in = "Hello, my name is John:";
char c = '*';
String [] words = {"hello","john"}; 

The desired output:

BufferedWriter out = "*Hello*, my name is *John*:";

The actual output:

BufferedWriter out = "*hello*, my name is *john*";

The code:

public void replaceString(BufferedReader in, BufferedWriter out, char c, String[] words){

String line_in = in.readLine();

    while (line_in != null) {
        for (int j = 0; j < words.length; j++) {

            line_in = line_in.replaceAll("(?i)" + words[j], bold + words[j]
                    + bold);

        }

        out.write(line_in);
        out.newLine();
        line_in = in.readLine();

    }
}